Preparation and separation of aromatic hydrocarbons



Nov. 19, 1940. c. R. WAGNER PREPARATION AND SEPARATION OF AROMATIC HYDROCARBONS Filed Jan. 29, 1937 mm Lw QNN Q K JINVIENTOIR B i LW 4 ATTORNEY Patented Nov. 19, 1940 PREPARATION AND snimnanon F anom'rrc nrnnooannons Cary R. Wagner, Chicago, 111., assignor to The Pure Oil Company, Chicago, 111., a corporation of Ohio Application January 29, 1931, Serial No. 122,914

3 Claims.

and stabilizing aromatic hydrocarbons and is more particularly concerned with the preparation and isolation of substantially pure aromatic hyl drocarbons.

It is known that aromatic hydrocarbons may be prepared by conversion of hydrocarbon gases. In my application Serial No. 85,711, flied June 17, 1936, there is disclosed a method for producing hydrocarbons by subjecting olefin containing gases to temperatures of approximately 1100 to 1200 F. under pressures up to approximately 250 pounds per square inch for a period of time ranging from approximately 5 to 30 seconds. When oleiinic gases are treated in accordance with the conditions of temperature pressure and time recited in the aforesaid application, a liquid product is obtained which is a mixture of henzene, toluene, xylene, and heavier aromatic hydrocarbons in which toluene and xylene are present in considerable quantities, together with oleiinic and dlolefinic hydrocarbons, with possible traces of paraiiinic and saturated or partly saturated cyclic hydrocarbons. The liquid may contain from 50 to 80% of aromatics, the major portion of the remaining being dioleflns.

The unsaturated, particularly the diolefinic, hydrocarbons present in the liquid mixture, have boiling points so close to those of the several 80 aromatic hydrocarbons present in the liquid that it is impossible to separate them from the aromatic hydrocarbons by fractional distillation or condensation. For example, 2,4-hexadiene boils between 80 and 82 C. and therefore cannotbe separated from benzene which boils at 80.1 C. The same applies to 3-methyl-2,4-'pentadiene which boils at 76 to 79 C.; S-methyl-l, 3-pentadiene which boils at 78 to 83 C.; and 1,2-hexadiene which boils at 78 C. Likewise, such compounds as 2,4-heptadiene which boils at 107 C.

and 3-methyl-2, 4-hexadiene whichboils at ill! to 108 C. are so close to toluene which boils at 110.B C. that satisfactory separation cannot be obtained by fractionation;

' from the value of thearomatic hydrocarbons whether used in admixture or separately. It is therefore necessary to separate the diolefins without materially affecting the aromatic constituents 5 present in the mixture. n

One of the objects of my invention is to eliminate the olefinic and dioleflnic hydrocarbons I without changing thearomatic constituents present in the condensate or liquid mixture. Another object of myinventionis to separate Moreover, the diolefinsiire unstable and detract This invention relates to a method of preparing substantially pure aromatic hydrocarbons such as benzene, toluene, xylene, and naphthalene from the liquid mixture.

Other objects of my invention will be apparent from the ensuing description and accompanying 5 drawing of which the single figure is a diagrammatic elevational view of apparatus suitable for carrying out the process.

I have discovered that the undesirable dioleflnic hydrocarbons present in the polymer condensate 10 can be converted to saturated compounds by proper hydrogenation so that the resulting product may be used as a motor fuel of high octane value, or the condensate may be fractionated into its various components. The hydrogenation may 15 be carried out as part of a unitary gas conversion and hydrogenation process, or may be carried out separately. In either case, the aromatic condensate, or fractions thereof, resulting from the conversion of the gases are treated with hydrogen 20'- at a temperature of about 350 to 800 F. and at pressuresup to pounds per square inch, in the presence of a mild hydrogenation catalyst such 'as nickel or nickel oxide. Under these conditions selective hydrogenation of the oleflnic and 25 leflnic hydrocarbons can be obtained if the quantity of hydrogen used is properly regulated. The amount of hydrogen to be used can be determined .by first determining the oleflnic and diolefinic content of the polymer condensate and then 80 treating the condensate with hydrogen in'slight excess (not substantially above 25% byvolume) of the quantity necessary to saturate the olefins and diolefins that are present. The hydrogenation step may be performed either in batch or in 86' hydrogenation above specified, the aromatics re;- main unchanged but the olefins and dioleflns are, 45

converted to saturated compounds which boil? at temperatures sufiiciently different from the boiling points of the aromatic hydrocarbons to enable fractionation of the hydrogenatedproducts into substantially pure benzene, toluene, 60,

xylene, naphthalene, etc. to be( effected. By

saturating '2A-hexadiene its boiling point ,is

changed from 80-82 C. to 69 0.; likewise 3- methyl-2,4-pentadiene is changed from 7649 C. to 60 0.; 2,4-heptadiene is changed from 107 55.

C. to 98.4 C.; 3-methyl-2,4-hexadiene is changed from 107-108 C. to 92 0.; 3-methyl-L3-pentadiene is changed from 78-83 C. to 63.2 C.; 1,2-hexadiene is changed from 78 C. to 69 C.

The character of aromatic polymer distillate will, of course, vary with the temperature and other conditions under which it is prepared. Although temperatures of 1100 to 1200 F., and preferably 1125" to-1150 F. and pressures up to 250 pounds per square inch with a reaction period of 5 to 30 secondsare prepared for obtaining large yields of toluene and xylene, it is to be understood that the temperature and pressure as well as time may vary from those given if large yields of toluene and xylene are not desired.

In order to avoid the likelihood that, upon hydrogenation certain of the diolefins or olefins having boiling points close to a higher boiling aromatic compound, may be converted into saturated compounds having boiling points fairly close to a lower boiling aromatic hydrocarbon, the polymer condensate should preferably first be fractionated into several cuts containing benzene, toluene, xylene, naphthalene, etc., respectively, together with those olefins and diolefins which boil close to the particular aromatics contained in the cut. Each fraction may then be separately subjected to hydrogenation conditions as above set forth, and after hydrogenation, subjected to individual fractionation to separate the saturated oleiins and diolefins from the single aromatic hydrocarbon present in the out. In this manner aromatic hydrocarbons of exceptional purity can be obtained which are valuable in the arts.

As previously stated, however, if it is not essential to recover pure aromatic hydrocarbons, the total polymer condensate may be subjected to selective hydrogenation to convert the diolefins and to some extent the olefins to saturated hydrocarbons so that the resulting product will be rendered gum and color stable and free from objectionable odor, without detracting from its anti-knock characteristics. The product so treated may be suitably fractionated to obtain a premium motor fuel having an octane rating of approximately 80 to 100.

In carrying out the process, hydrocarbon gas having an olefin content of approximately 40-60% is charged through line I by means of compressor 3 into heating coil 5 and reaction zone I. The gases are heated to reaction temperature in the heating coil, which may be approximately 1100 to 1200 F. under a pressure ranging from atmospheric to approximately 250 pounds per square inch, and then chargedunder these conditions through the reaction zone, which may be a coil or reaction chamber, in order to give the gas sufllcient time to polymerize.- From the reaction zone the reaction products pass through outlet 9 controlled by valve I in separator II and are chilled by a stream of liquid which is pumped from the bottom of separator II by means of pump I2 through line I3 and line I4 controlled by valve I5, to the outlet line 9. Pressure on the reaction products may be released at valve I0 below that in the reaction zone. The portion of the liquid which is not used as chilling stock is pumped through line I6 controlled by valve and joins the gas coming off the top of separator II through line I8. The mixture of liquid and gas enters the fractionating tower I9 through line 2|.

The incondensible constituents in the mixture pass overhead from the fractionating tower I9 through line 23 and condenser 25 to accumulator and gas separator 21. The uncondensed constituents leave the top of the separator 21 through line 29 controlled by valve 3|, and may be withdrawn from the system. The condensed constituents are recycled from the separator 21 through line 33 to the top' of the fraotionator I3 to act as reflux. The unvaporized products may be withdrawn from the lower part of the fractionator I9 through line 35 controlled by valve 36 and passed into a second fractionating tower 31. Any tarry material that may collect in the Iractionator I9 may be withdrawn from the bottom thereof through the line 30, controlled by valve 4|.

The liquid in the fr'actionating tower 31 may be heated by reboiler 43 to a temperature suflicient to vaporize benzene, toluene, xylene, naphthalene and other hydrocarbons boiling within the range of these constituents. The

benzene, toluene, xylene and naphthalene are withdrawn as side cuts-from the fractionating tower 31 through valve-controlled lines 45, 41, 49, and respectively. Any material boiling above naphthalene maybe withdrawn from the fractionating tower 31 through the line 53 controlled by valve 55. -Those constituents boiling below benzene may be withdrawn from the top of the fractionating tower 31, through line 51, and passed through condenser 59 into accumulator 6|, from which the liquids maybe withdrawn through lines.63 controlled by valve 65, and any gaseous material may be withdrawn through line 61 controlled by valve 69. If desired, the pressure on the fractionating system may be maintained at super-atmospheric pressure sufliciently high to enable the several cuts to be charged to the subsequent hydrogenation steps without the necessity of pumping. In that case the pumps may be dispensed with or by-pass lines provided around the pumps.

The benzene cut which may have 'a boiling range of from approximately 165 F. to approximately 181 F., may be charged through line 45 by means of pump 1| to heating coil 13 wherein it is heated to a temperature of approximately 350' to 800 F. and then fed into the reactor 15 which contains the hydrogenating catalyst. Hydrogen, or a gas rich in hydrogen, is fed into the reactor through line 1'! controlled by valve 19. The products leave the reactor I5 through line 8| controlled by valve 83 and p'assinto a fractionating tower 85, wherein the benzene is separated from contaminating constituents. The benzene may be withdrawn as a' side stream through line 8! controlled by valve 89; overhead products may be withdrawn through line 3|, condenser 93, to a separator 95, from which gases are withdrawn through line 91, controlled by valve 99, and condensate is "withdrawn through line I0| controlled by valveI03; and constituents heavier than benzene are withdrawn through line I04 controlled by valve I05. a

The toluene out having a boiling range-between. about 227 F. and 235 F., is similarly charged from line 41 by means of pump I06 through heating coil I01, reactor I09, line III controlled by valve I I3, to fractionator H5. The toluene is withdrawn from the fractionator as a side stream through line controlledby valve H9. The fractions boiling above toluene are withdrawn from the fractionating tower H5 through line I2I controlled by valve I23, and the fractions lighter than toluene are withdrawn through line I25, condenser I21, into separator M9. The liquid collected in separator I29 is withdrawn therefrom through line I3I, controlled by valve I 33,- and the gases are withdrawn through 5 line I35 controlled by valve I31.

The xylene out having a boiling range between about 267 F. and 282 F., is charged from line 49 by means of pump I49 into heating coil I5I through reactor I53, line I55, controlled by valve I51, to fractionator I59. The xylene is withdrawn as a side stream from fractionator I59 through line I8! controlled by valve I63. Constituents boiling above xylene are withdrawn from the fractionator through line I65 controlled by valve I61, and the constituents boiling below xylene are withdrawn from the fractionator through line I89 and condenser I1I into separator I13. The liquids collected in I13 may be withdrawn therefrom through line I15 controlled by valve I11. Gases may be withdrawn from the separator I13 through line I19 controlled by valve I8I.

The naphthalene cut is charged from line Si by means of pump I83 through heating coil I85, reactor I81, line I89 controlled by valve I9I, into fractionator I93. The naphthalene may be withdrawn from the fractionator I93 as a side out through line I95 controlled by valve I91. Fractions heavier than naphthalene may be withdrawn from the fractionator through line I99 controlled by valve 29!. naphthalene may be withdrawn from the fractlonator through line 203 and condenser 295 into separator 281. Liquids may be withdrawn from the separator through line 289 controlled by valve 2| I, and gases may be withdrawn through line 2| 3 controlled by valve 2| 5. Hydrogen, or gas rich in hydrogen, may be fed into the reactors I89, I53, and I81 through valve-controlled 40 lines 2", 2I9, and 22I respectively.

If it is not desired to separate the several cuts prior to hydrogenation, the polymer condensate may be withdrawn from fractionator I9 through line 35 and charged through line 223 controlled 45 by valve 225,'by means of pump 221, into the heating coil 229 and catalyst chamber or reactor 23L reactor through line 233 controlled by valve 235.

The reaction mixture is discharged from the re- 50 actor through line 231 controlled by valve 239,

into fractionator ,2. The reaction products may be fractionated in 2 in order to obtain an overhead distillate suitable as motor fuel, which may be withdrawn through line 243, through con- 65 denser 245, into accumulator and separator 241. From the accumulator 241 the finished motor fuel may be withdrawn through line 249 controlled by valve 25I, and the gases may be withdrawn through line 253 controlled by valve 255. Liquids 60 heavier than those suitable for motor fuel may be withdrawn from the fractionator 24l through line 251 controlled by valve 259.

If it is desired to separatebenzene, toluene, xylene, and naphthalene, or any one of them,

5 these compounds may be separated as side streams from the fractionating tower through the valve-controlled side stream withdrawal lines 26 I 293, 285, and 281 respectively.

Fractions boiling below Hydrogenating gas may be fed into the- The apparatus shown and described herein is for the purpose of illustration only. It will be understood that the method may be carried out in any suitable apparatus and that the polymerization of the gases to liquid may be carried out as a separate and distinct operation from the hydrogenation and fractionation of the resulting products.

In accordance with my invention, I am enabled to increase the yield of high octane gasoline without destroying the anti-knock rating thereof and at the same time obtain a product which is stable as to gum and color and free of objectionable odor; or as an alternative I am enabled'to produce substantially pure aromatic hydrocar-- bons without decreasing the quantity thereof present in the original mixture.

I claim as my invention:

1. The method of preparing substantially pure aromatic hydrocarbons from mixtures containing predominantly aromaticv liquid hydrocarbons produced by subjecting olefin-containing hydrocarbon gases to temperatures of approximately 1100 to 1200 F. at pressures up to approximately 250 pounds per square inch for a period of time ranging from approximately five to thirty seconds, which comprises separating the mixtures into a plurality of fractions each having a narrow boiling range closely approaching the boiling point of an aromatic hydrocarbon, separately subjecting said fractions to selective hydrogenation under conditions whereby to hydrogenate unsaturated non-aromatic compounds contained therein in order to lower the boiling points of said compounds without substantially affecting the aromatic hydrocarbons and separately fractionating the hydrogenated products to obtain substantially pure aromatic hydrocarbons.

2. Method in accordance with claim 1 in which the hydrogenation is carried out at temperatures between 350 and 800 F. and under pressures up to 100 pounds per square inch in the presence of a mild hydrogenating catalyst.

3. The method of preparing substantially" pure aromatic hydrocarbons from mixtures containing predominantly aromatic liquid hydrocarbons produced by subjecting olefin-containing hydrocarbon gases to temperatures of approximately 1100 to 1200 F. at pressures up to approximately 250 pounds per square inch for a period of time ranging from approximately five to thirty seconds, which comprises separating the mixtures into at least three fractions having boiling ranges between approximately 165-181 F., 221-235 F. and-26'7-282" F., respectively, separately subjectmg each fraction to selective hydrogenation at temperatures between 350-8001F. and under pressures up to 100 pounds per square inch in order to convert non-aromatic hydrocarbons having boiling points closely approaching that of the aromatic hydrocarbons in the particular fraction into hydrocarbons whose boiling points diifer more widely from that of the aromatic hydrocarbons, and subjecting the hydrogenated. fractions to careful fractionation in order to separate the aromatic from the non-aromatic hydrocarbons.

CARY R. WAGNER. 

